More bash commands

Bash Head

head is used to print the first ten lines (by default) or any other amount specified of a file or files. cat, on the other hand, is used to read a file sequentially and print it to the standard output (that is, it prints out the entire contents of the file).

That is not always necessary, though – perhaps you just want to check the contents of a file to see if it is the correct one, or check that it is indeed not empty. The head command allows you to view the first N lines of a file.

If more than on file is called, then the first ten lines of each file is displayed, unless a specific number of lines are specified. Choosing to display the file header is optional using the option below.

Usage

head [options] [file_name(s)]

Most used options:

-n N, prints out the first N lines of the file(s)

-q, doesn’t print out the file headers

-v, always prints out the file headers

Example

head file.txt

Prints the first ten lines of file.txt (default)

head -n 7 file.txt

Prints the first seven lines of file.txt

head -q -n 5 file1.txt file2.txt

Prints the first 5 lines of file1.txt, followed by the first 5 lines of file2.txt

Bash mv

This bash command moves files and folders.

mv source target
mv source ... directory

The first argument is the file you want to move, and the second is the location to move it to.

Commonly used options:

-f to force move them and overwrite files without checking with the user.

-i to prompt confirmation before overwriting files.

Bash Cat

cat is one of the most frequently used commands in Unix operating systems.

cat is used to read a file sequentially and print it to the standard output. The name comes from the way it can concatenates files.

Usage

cat [options] [file_names]

Most used options:

-b, number non-blank output lines

-n, number all output lines

-s, squeeze multiple adjacent blank lines

-v, display nonprinting characters, except for tabs and the end of line character

Example

Print the content of file.txt:

cat file.txt

Concatenate the content of the two files and display the result in terminal:

cat file1.txt file2.txt

More info on Bash:

What is Bash?

Bash (short for Bourne Again SHell) is a Unix shell, and a command language interpreter. A shell is simply a macro processor that executes commands. It’s the most widely used shell packaged by default for most Linux distributions, and a successor for the Korn shell (ksh) and the C shell (csh).

Many things that can be done in the GUI of a Linux operating system can be done via the command line. Some examples are:

Using bash on the command line (Linux, OS X)

You can start using bash on most Linux and OS X operating systems by opening up a terminal. Let’s consider a simple hello world example. Open up your terminal, and write the following line (everything after the $ sign):

zach@marigold:~$ echo "Hello world!"
Hello world!

As you can see, we used the echo command to print the string “Hello world!” to the terminal.

Writing a bash script

You can also put all of your bash commands into a .sh file, and run them from the command line. Say you have a bash script with the following contents:

#!/bin/bash
echo "Hello world!"

This script only has two lines. The first indicates what interpreter to use to run the file (in this case, bash). The second line is the command we want to use, echo, followed by what we want to print, here, "Hello world!"

It’s worth noting that first line of the script starts with #!. It is a special directive which Unix treats differently.

Why did we use #!/bin/bash at the beginning of the script file?

That is because it is a convention to let the interactive shell know what kind of interpreter to run for the program that follows.

The first line tells the operating system that the file should be executed by the program at /bin/bash, the standard location of the Bourne shell on almost every Unix or Unix-like system. By adding #!/bin/bash at the beginning of the script, it tells the OS to use the shell at that specific path to execute all the following commands in the script.

#! goes by many names such as "hash-bang", "she-bang", "sha-bang", or "crunch-bang". Note that this first line is only considered if the script is an executable.

For example, if myBashScript.sh is executable, the command ./myBashScript.sh will cause the OS will look at the first line figure out which interpreter to use. In this case it would be #!/bin/bash.

On the other hand, if you run bash myBashScript.sh, then the first line is ignored since the OS already knows to use bash.

To make myBashScript.sh executable, simply run sudo chmod +x myBashScript.sh. Then run the following command to execute the script:

zach@marigold:~$ ./myBashScript.sh
Hello world!

Sometimes the script won’t be executed, and the above command will return an error. It is due to the permissions set on the file. To avoid that, use:

Our mission: to help people learn to code for free. We accomplish this by creating thousands of
videos, articles, and interactive coding lessons - all freely available to the public. We also have
thousands of freeCodeCamp study groups around the world.

Donations to freeCodeCamp go toward our education initiatives, and help pay for servers, services,
and staff.